Dams and reservoirs on the Columbia and Kootenay river systems generate about half the hydroelectricity produced in BC. Water stored in reservoirs behind dams is also released to meet our needs for flood control, fisheries, irrigation, recreation and transportation.
This means water levels can change—sometimes over the course of a day and sometimes gradually over the year. Generally, water is released and reservoirs are drawn down in winter to meet the need for hydroelectricity. In spring, melting snow refills the reservoirs.